1. Field of the Invention
Disclosed herein are photoelectrocatalytic devices and methods, including multi-junction artificial photosynthetic components and methods of use and manufacture thereof.
2. Description of the Related Art
Development of an inexpensive solar fuel conversion process for the cleavage of water and CO2 reduction could potentially generate fuels or industrial chemicals with net zero carbon emissions. Based on the thermodynamic requirements alone, solar radiation with photon energies greater than 1.23 electron-volts is required to split water or to reduce CO2 to fuels. However, water oxidation at photo-anode is a kinetically sluggish process and likewise CO2 reduction at photo-cathode needs high overpotentials, resulting in actual energy requirements greater than 2.0 V. Therefore, using a single light absorber unit for water splitting or CO2 reduction requires a semiconductor with large band gap (Eg>2.5 eV), limiting the exploitation of a substantial portion of the solar spectrum.
Several strategies have been pursued to increase the obtainable phovoltages while maximizing sunlight absorption. One strategy is the use of multijunction/tandem photovoltaic designs to convert a large portion of the terrestrial solar spectrum into high free energy materials that can be used as fuels and chemicals. It has been estimated that these strategies are capable of achieving ˜18% solar-to-hydrogen conversion efficiencies. Rocheleau, R. & Miller, E. Energy Fuels 12, 3 (1998). Indeed, John Turner and his colleagues have already demonstrated a solar-to-H2 conversion efficiency of 12.4% using multi junction III-V semiconductors in 1990's. Khaselev, O. & Turner, J. Science 280, 425 (1998). However, the high costs and complexities associated with device fabrication using triple junction a-Si, (Weber, M. & Dignam, M. J. Electrochem. Soc. 131 (1984)), and III-V semiconductors have prevented from commercial realization. Moreover, their stable operation in harsh electrochemical conditions for long hours remains insufficient.
Accordingly, there has been and remains a need to find reliable photoelectrochemical devices and methods for novel, carbon-neutral energy cycles using only sunlight as the energy input for solar-driven production of fuels and chemicals. Such devices and methods should be able to provide sufficient photovoltages while maximizing sunlight absorption. In addition, such devices and methods should resist the corrosive effects of a harsh electrochemical environment.